An ion with a charge of +3.2×10−19 C is in region where a uniform electric field of 5×104 V/m is perpendicular to a uniform magnetic field of 0.8 T. If its acceleration is zero then its speed must be: 0 m/s 1.6×10−5 m/s 4.0×105 m/s 6.3×104 m/s any value but 0 m/s